The present invention relates to viscous couplings, and more particularly, to such couplings employed in automatic transmission torque converters, to serve as by-pass elements, by-passing the torque converter.
Torque converter type automatic transmissions have achieved widespread application and acceptance in motor vehicles. Although generally satisfactory in this application, torque converter type automatic transmissions inherently involve a certain amount of slippage, and therefore, inherently result in losses in vehicle fuel economy. In an effort to minimize such slippage, and thereby increase fuel economy, efforts have been made to by-pass the torque converter with some type of relatively direct drive, which typically is activated when the vehicle is operating in the higher gear ratios, and above a predetermine vehicle speed.
While such prior art direct drive by-pass arrangements have resulted in improvements in fuel economy, certain types of by-pass elements utilized have, under certain operating conditions, transmitted various driveline vibrations to the passenger compartment of the vehicles, causing degradation of the ride quality of the vehicle.
In an effort to provide a by-pass element which would not transmit driveline vibration to the passenger compartment, those skilled in the art have utilized a viscous coupling as the by-pass element. Although the use of a viscous coupling as the by-pass element does serve to minimize the transmission of driveline vibration, it is still important that the coupling be designed for maximum durability and, at the same time, reliable and inexpensive manufacture.
A typical prior art viscous coupling of the type to which the present invention relates is illustrated and described in U.S. Pat. No. 4,462,492, assigned to the assignee of the present invention, and incorporated herein by reference. Such couplings include a pair of sidewalls which are journalled on a clutch hub by means of a pair of bushings. Typically, and as is shown in the above-incorporated patent, the bushings are of substantially the same size. However, as is well known to those skilled in the art, these two bushings have had to be of different construction, because of the differences between them in regard to the ability to permit the flow of fluid therethrough.
Having two bushings, which differ in construction, but are the same or substantially the same in diameter, can result in errors during assembly, or alternatively, may necessitate a more complex and expensive assembly process. In the viscous couplings which are in commercial production, reversal of the bushings during assembly could result in the presence of ATF (automatic transmission fluid) within the seal chamber of the coupling, at an undesirably high pressure.